White noise switching system for percussion tone synthesis

ABSTRACT

A switching system in which a wave clipping circuit removes one side of a white noise signal, and a switching circuit switches this one-side-removed signal in accordance with bias control between a conducting region and a cutoff region, the white noise signal wave being caused to enter the cutoff region from the notremoved side during the signal attenuation process in the switching circuit.

United States Patent [72] Inventor Yasunori Hirose Shizuoka-ken, Japan [21] Appl. No. 794,947

[22] Filed Jan. 29, 1969 [45] Patented Mar. 16, 1971 [73] Assignee Nippon Gakki Selzo Kabushiki Kaisha Nakazawa-cho. Hamamatsu-shi, Shizuoka-ren, Japan [32] Priority Jan. 30, 1968 [33] Japan [54} WHIT E NOISE SWITCHING SYSTEM FOR PERCUSSION TONE SYNTHESIS [50] Field ofSearch 84/1.01, 1.03,1.17,1.24,1.25,1.26,50,1.11,l.12,1.19, 1.21; 307/106, 237, 260, 2613;328/165, 167;

3,140,336 7/1964 Campbell.... 3,328,506 6/1967 Park Primary Examiner-D. F. Duggan A rtorney- Holman & Stern ABSTRACT: A switching system in which a wave clipping circuit removes one side of a white noise signal, and a switching circuit switches this one-side-removed signal in accordance 4 Claims 12 Drawing Figs with bias control between a conducting region and a cutoff re- [52] US. Cl 84/ 1.19, gion, the white noise signal wave being caused to enter the cu- 84/ 1.26, 340/384 toff region from the not-removed side during the signal at- [51] Int. Cl.. 61% 1/02 tenuation process in the switching circuit.

WE WAVE ITCHING NOISE 5w GENERATOR 2* CLIPPER i CIRCUIT T F'LTER '3 Patented March 16, 1971 I 3,571,484

3 Sheets-Sheet 1 F I G. l

PRIOR ART 'I IIII lgl awit nh "5 II W ICUT-OFF REGION I MDUCTING REGION I 3 4 WHITE 3 WAVE SWITCHING YGENNEIIRSAETOR fi CL'PPER E CIRCUIT T FILTER l I I o d I I I INVENTOR 1M0 Patented March 16, 1971 3,571,484

3 Sheets-Sheet 2 CUT- OFF FIG. 4(d) ATTORNEYS Patented March 16, 1971 3,571,484

3 Sheets-Sheet 3 FIG. 6(0) FIG. 6(0) FIG. 6(d) CONDUCTING REGION LL. 6 t i LIJ LLI X X .INVENTOR BY% JM DM%A-7 AT'TOR NEYS WHITE NOISE SWITCHING SYSTEM FOR PERCUSSION TONE SYNTHESIS BACKGROUND OF THE INVENTION This invention relates generally to electronic musical instruments and more particularly to a new white noise-switching system in which tone color variation does not occur in the attenuation processof a white noise signal, and in which signal leakage is substantially reduced.

In general, white noise is frequently used when sounds of percussion instruments (for example, sounds of cymbals and maracas) and simulated sounds (for example, sounds of sea waves and wind) are to be produced in electronic musical instruments. The reason for this is that percussion instrument sounds and simulated sounds in most cases do not have specific frequencies but contain numerous frequency components, whereby it is convenient to use white noise.

However, the amplitude of white noise continually varies in an irregular manner, presenting a coarse envelope. For this reason, when white noise is passed directly (without modification) through a switching circuit of the type widely used heretofore in electronic musical instruments, that is, a switching circuit in which a bias is controlled to cut off the white noise from one side of the white noise signal wave, a great waveform variation (that is, tone color variation) unavoidably occurs in the attenuation process of the white noise signal wave after keying off because the lastly remaining portion of the signal consists of lower peaks of the wave which are irregular and very intermittent as indicated in FIG. 1.

Such a phenomenon is particularly conspicuous in cases wherein the attenuation time is relatively long as in the case of a cymbal sound (emitted when a cymbal is struck by a stick or when cymbals clash together), whereby it is extremely difficult to reduce such use of white noise and the means therefor to practice.

For this reason, it has heretofore been a common practice to cut off the white noise signal wave from both sides by using a variable gain push-pull amplifier such as a balanced modulator thereby to prevent the occurrence of waveform variation during attenuation. This practice, however, has given rise to the disadvantage of high cost of the apparatus itself.

Accordingly, a white noise keying system of simple organization whereby the above-described difficulties are overcome and, in the switching of a white noise, the white noise component is sustained to the end in the attenuation process thereof is desired.

As a result of my experimental studies, I have ascertained that, in the case wherein a white noise is used as one of the tone sources or tone generators of an electronic musical instrument, and when the amplitude of the white noise is suitably limited, there is a range wherein there is no sensible change in the tone color thereof.

SUMMARY OF THE INVENTION It is an object of the present invention to utilize the above described findings to overcome the aforedescribed difficulties in the prior art and to provide a white noise-switching system of simple organization in which, in the switching of white noise, the white noise component is sustained up to the extreme end of the attenuation process of the switching operation.

Another object of the invention is to provide a white noiseswitching system wherein signal leakage is substantially reduced.

The foregoing object of the invention has been achieved by a system wherein the white noise remaining after removal of a substantial amount of one side of the signal or the white noise remaining after removal of a whole of one side and a part of the other side is switched thereby to reduce the signal leakage.

According to the present invention, briefly summarized, there is provided a white noise-switching system characterized by the combination of a wave-clipping means for amplitude limiting a white noise signal to produce an output signal having a coarse wave side and a smooth wave side, and a switching means for switching this output signal in accordance with bias control between a conducting region and a cutoff region, the white noise signal wave being caused to enter the cutoff region from the coarse side of the clipped white noise signal in the signal attenuation process in the switching means.

The nature, principle, details, and utility of the invention will be more clearly apparent from the following detailed description with respect to a preferred embodiment of the invention when read in conjunction with the accompanying drawing, in which like parts are designated by like reference numerals and characters.

BRIEF DESCRIPTION OF THE DRAWING In the drawing FIG. I is a graphical representation, with time as the abscissa, indicating the output waveform of a white noise-switching system of known type;

FIG. 2 is a block diagram indicating the essential organization of a white noise-keying system embodying the invention connected to a white noise generator;

FIG. 3 is a schematic diagram showing the details of one example of circuit organization for the white noise-keying system shown in FIG. 2;

FIGS. 4(a), 4(b), 4(0), and 4(d) are graphical representations, with time as the abscissa, respectively indicating signal waveforms at various parts of the circuit shown in FIG. 3;

FIG. 5 is a schematic diagram showing another embodiment of the invention; and

FIGS. 6(a), 6(b), 6(c), and 6(d) are graphical representations, with time as the abscissa, respectively indicating signal waveforms at various parts of the circuit shown in FIG. 5.

DETAILED DESCRIPTION Referring to FIGS. 2 and 3, white noise is supplied by a white noise generator I operating to amplify noise generated by electronic components such as transistors and diodes and thereby to produce white noise. At the output terminal a of this white noise generator I, there is produced a white noise of a waveform as indicated in FIG. 4(a).

This output white noise is transmitted to a wave clipper 2 consisting of a B-class or Cclass amplifier, which operates to remove a substantial amount of one side thereof. At the out put terminal b of this waveform converter 2, there is produced a signal as indicated in FIG. 4(1)), that is, a signal of constant potential on its upper side and an irregular potential on its lower side.

This output signal ofthe wave clipper 2 is sent to a switching circuit 3 forming an envelope of the resultant output signal by controlling the bias of a transistor (or some other component such as a diode or a vacuum tube). This switching circuit 3 accomplishes bias control in a manner such that the aforementioned irregular signal enters the cutoff region from the side opposite that which has been removed by wave clipper 2, that is, the coarse side, as indicated in FIG. 44(0).

A signal produced in this manner contains an abundant quantity of components of various frequencies similarly as the original white noise and amply possesses the features of a white noise throughout the end of the signal decay, that is, the time at which the entire signal is cutoff.

The output signal of this switching circuit 3 is sent to a filter circuit 4, where it is rendered into the tone color of the desired percussion instrument sound or simulated sound, and a signal of a waveform as indicated in FIG. 4(d) is produced at output terminal d of the filter circuit 4.

l have confirmed further that small part could be cut off from the coarse side of the above-mentioned one-side-clipped signal, by clipping rare but large peaks of the signal, with the tone color effected substantial no change and the disposition of the signal in the following stages of the circuit becoming convenient.

FIG. 5 shows another embodiment of this invention differing from FIG. 3 at the wave clipper 2 and the switching circuit 3. The wave clipper 2 operates to remove a half wave or one side of the mean direct-current level of the white noise signal together with a part (30 percent for example) of the other side below level K in FIG. 6(b). As the amplitude of the signal applied to the input side of the switching circuit 3 is limited within a certain amount, it becomes possible to reduce the signal leakage which appears on the output side and also to connect the collector of the transistor of the wave clipper 2 to the base of the transistor of the switching circuit 3 as shown in FIG. 5. FIG. 6(0) and 6(d) show, respectively, the waveforms at points c and d of FIG. 5.

When a system of the above-described organization according to the invention is used to switch signal which contains abundantly different frequency components as in the case of a white noise and, moreover, has an amplitude which continually varies in an irregular manner, there is no remarkable tone variation in the attenuation process, and, moreover, the signal leakage in the switching circuit is also very small. Therefore, desired percussion instrument sounds and simulated sounds can be readily produced.

lclaim:

1. A white noise-switching system comprising, in combination, a white noise generator for generating a white noise signal having an irregular amplitude presenting a coarse envelope, electrical wave-clipping means coupled to said white noise generator for amplitude limiting a substantial amount of only one side of the white noise signal and for thereby producing an output signal having an envelope with a smooth side and coarse side, and electrical-switching means coupled to said wave-clipping means, said electrical switching means defining a conducting region and a cutoff region thereof and incorporating a biasing control means therefor, said biasing control means attenuating the output signal from said clipping means by switching the output signal from the conducting region to the cutoff region of said switching means with the output signal entering the cutoff region of said switching means from the coarse side of its envelope.

2. A white noise-switching system comprising, in combination, a white noise generator for generating a white noise signal having an irregular amplitude presenting a coarse envelope, electrical wave circuit means coupled to said white noise generator for removing all of only one side of a mean direct-current level of the white noise signal and for amplitude limiting the other side of the white noise signal to a predetermined level thereby producing an output signal having an envelope with a relatively smooth side and a relatively coarse side, and electrical-switching means coupled to said wave clipping circuit means, said switching means defining a conducting region and acutoff region thereof and incorporating a biasing control means therefor, said biasing control means attenuating the output signal from said wave-clipping circuit means by switching the output signal from the conducting region to the cutoff region of said switching means with the output signal entering the cutoff region from the relatively coarse side of its envelope.

3. A white noise-switching system comprising, in combination, a white noise generator for generating a white noise signal having an irregular amplitude presenting a coarse envelope, electrical wave-clipping circuit means coupled to said white noise generator for amplitude limiting only one side of the envelope of the white noise signal to thereby produce an output signal, and electrical switching means coupled to said wave clipping circuit means, said switching means defining an operational region and a cutoff region thereof and incorporating a biasing control means therefor, said biasing control means attenuating the output signal from the operational region to the cutoff region of said switching means with the output signal entering the cutoff region of said switching means from the amplitude limited side of its envelope.

4. A white noise-switching system as defined in claim 1, further including a filter circuit coupled to the output side of said switching circuit means. 

1. A white noise-switching system comprising, in combination, a white noise generator for generating a white noise signal having an irregular amplitude presenting a coarse envelope, electrical wave-clipping means coupled to said white noise generator for amplitude limiting a substantial amount of only one side of the white noise signal and for thereby producing an output signal having an envelope with a smooth side and coarse side, and electrical-switching means coupled to said wave-clipping means, said electrical switching means defining a conducting region and a cutoff region thereof and incorporating a biasing control means therefor, said biasing control means attenuating the output signal from said clipping means by switching the output signal from the conducting region to the cutoff region of said switching means with the output signal entering the cutoff region of said switching means from the coarse side of its envelope.
 2. A white noise-switching system comprising, in combination, a white noise generator for generating a white noise signal having an irregular amplitude presenting a coarse envelope, electrical wave circuit means coupled to said white noise generator for removing all of only one side of a mean direct-current level of the white noise signal and for amplitude limiting the other side of the white noise signal to a predetermined level thereby producing an output signal having an envelope with a relatively smooth side and a relatively coarse side, and electrical-switching means coupled to said wave clipping circuit means, said switching means defining a conducting region and a cutoff region thereof and incorporating a biasing control means therefor, said biasing control means attenuating the output signal from said wave-clipping circuit means by switching the output signal from the conducting region To the cutoff region of said switching means with the output signal entering the cutoff region from the relatively coarse side of its envelope.
 3. A white noise-switching system comprising, in combination, a white noise generator for generating a white noise signal having an irregular amplitude presenting a coarse envelope, electrical wave-clipping circuit means coupled to said white noise generator for amplitude limiting only one side of the envelope of the white noise signal to thereby produce an output signal, and electrical switching means coupled to said wave clipping circuit means, said switching means defining an operational region and a cutoff region thereof and incorporating a biasing control means therefor, said biasing control means attenuating the output signal from the operational region to the cutoff region of said switching means with the output signal entering the cutoff region of said switching means from the amplitude limited side of its envelope.
 4. A white noise-switching system as defined in claim 1, further including a filter circuit coupled to the output side of said switching circuit means. 